Method of and means for determining phase difference



@Qi. 7 1924-. v E. MERRITT METHOD OF AND MEANS FOR DETERMINING PHASE DIFFERENCE Filed July 1 1921 mum NOON

@922 yen 2-02 (Ernest Werrzi? Patented Oct. 7, 1924.

UNITED STATES ERNEST Illll:IFERLEIJIZIT OF- ITHACA, NEW YORK.

METHOD OF AND MEANS FOR DETERMINING PHASE DIFFERENCE.

Application filed July 1,

To all whom it may concern."

Be it known that I, ERNEST MERRITT, a citizen of the United States, residing at Ithaca, in the county of Tompkins and State of New York, have invented certain new and useful Improvements in Methods of and Means for Determining Phase Difference, of which the following is a'specification.

My invention relates to methods of and means for determining phase difference and a particular object thereof is to determine the phase difference at relatively high frequencies.

One of the important applications of the invention is to determine the direction of waves by means of phase difference but the principle involved in the invention contemplates numerous other applications.-a ml it therefore is my intention to claim my invention broadly as a system of phase determination, without any limitation as .to the particular application of the system.

The fundamental principle involved is the determination of phase differences between trains of waves or vibrations, by means of the phase difference between the beats that are. produced when these Wave" trains or vibrations are combined, by the do process OfheterOdyning, with another wave tram or vlbratlons of a different frequency.

l =a cos 21rnt+c cos (21rmt+0) 1921. Serial No. $81,935

It will be understood, of course, that it is immaterial whether the waves are electrical, mechanical or acoustical.

To illustrate the underlying principle of 'the method by which the phase difference between beats may be utilized to determine the phase difference betweentwo vibrations, consider the special case of two alternating currents, I and I of the same frequency n but, in general, of differentamplitude and phase; \Ve may put l za cos 21m: I :b cos (21c-nt+ p) The phase difference, cp, between the two currents is to be determined.

If each of the two currents is hetero dyned with a third current, 1 of frequency m the result will be the production of two currents I and I I being proportional to I -l-I and I proportional to 1 -1-1 Heterodyning might be effected by coupling bot-h I and I to some fourth circuit, in which case 1 is the current in this circuit. while I is the current in a circuit to which I and I are coupled. We have therefore (1) I :I +I :a cos Q-rmt-l-c cos (Qamt it [cos 211-0112 cos (21r'mt+0)] (c a) cos (21r mt 0) (3) =2a cos (215%2-3) cos I n-m I 0 (4) I 2b cos (211' 2 1+g-2 of the first factor in the expression for I in (3) is small while the frequency 2 of the second factor is relatively large.

cos (21r +g+g)+ (c-b) cos (21rmt+0).

The first term in this expression therefore represents a current of frequency Whose amplitude is changing with the frequency With a suitable detector this changing amrent of frequency plitude would give rise to beats, or, if sufficiently rapid, to a beat tone. The second term of (3) represents a current of constant amplitude and frequency m would be readily distinguished from the beating cur- In radio work it would usually be above the audible range.

Equation (4) shows that I, also consists of'a current of frequency m and constant amplitude, and a current of frequency whose amplitude changes with the frequency nm 0 Y Ti While in. the case of I the maximum occurs when Tw n- The difference in phase between the beats or beat ltones is therefore half as great as that between the original currents I and I rents.

are in phase.

By determining the phase difference between the beats We are thus able to determine the phase diflerence between the original cur- And if we adjust the phase of one of the currents until the beats are in phase we know that the two currents themselves Although in the fore oing illustration the two vibrations whose ifi'erence in phase is to be determined are assumed to: be alterpating electric currents, yet-it is clear that the same principle would apply in dealing with acoustic vibrations or trains of waves, or with vibrations of a pure-mechanicaltype. It is clear also that the principle is the same whatever may be the frequency of the original vibrations or of the vibration used in the process of heterodyning.

The best method of determining the phase difference between the beats will depend upon the rapidity with which the beats occur ployed in each particular case. For example, if the beats occur so slowly that they can be separately obserwed any method may be used. that is suitable for the measurement of rather short intervals of time. If the beats are so rapid as Ito produce an audible tone an acoustic compensator may be used 1. e. the two tones may be brought to the ear, or other receiving device, b tubes of variable length and the length 0 one or both may be altered until the two sounds reach the ear in the same or in opposite phase. The first case is recognized by a maximum, the second by a minimum, of

loudness. In certain cases I have found it advantageous to use the binaural principle as a means of estimating equality or inequality of phase; i. e..one beat tone is brought to the right ear and the other to the left; if the phase is the same for both the sound will appear to be directly in front of the observer.

If two suflicientl'y spaced collectors, such as antennae, quartz crystals, or diaphragms, are acted upon by a train of waves coming in any direction, other than at right angles to the line joining the two collectors, the receivedcurrents will differ in phase by an amount dependin upon the direction, the distance apart of the collectors, and the wave length. It is an important application'of the present invention to determine this phase difference and by means of it the direction of the train ofwaves.

Heretofore it has been difficult to determine the phase difference of currents of high radio fr uencies, while the time interval correspon ing to the ph'ase difference between two beat Itones is relatively large. Since the phase difference between the beat tones is always one half of the phase difference between the original vibrations, and

since the frequency of the'beats can be made as small as desired, it will be seen that theoretically there is no limit to the time amplification the method permits, except of course,'such as is due to the impossibility of maintaining constant frequencies, and other like difiiculties I will now describe in detail one method by which my invention may be employed in recognizing and determining the phase difference between It-he received currents oh two wave collectors, the ultimate urpose being to determlne the direction om which the signals oomeor to distinguish-between and upon the nature of the vibrations emsignals from different directions.

The Figure is a diagrammatic view of the system:

Numerals l and 2 refer to two antennae which are preferably exactly alike, and at a distance apart which is an appreciable fraction of a half wave length of the waves employed. It will be understood that in place of the antennae shown, any form of collectors may be employed, such as quartz tuned oscillatory circuit 9, having a source of undamped oscillations 10, is coupled to both of the circuits 3 and at, by means of the variable couplings 13 and 14. A vacuum tube oscillaton serves well as the source of oscillations 10.

Each of the circuits 3 and 4 is provided with a telephone receiver, indicated by numeral 7 and 8.

In operation, the incoming wave trains are collected by the two antennae and are heterodyned by the local oscillatory circuit 9, thereby producing beat tones in the circuits 3 and 4. If the two telephone receivers are now brought to the ears, the phase difference will show itself by the binaural sense, and signals from different stations may be distinguished by the fact that the sounds appear to come from different directions. If proper compensating means is provided in the system, the two currents may be brought into phase, the phase difference thus being measured.

To bring about this phase compensation the electric compensators 11 and 12-inay be used as shown as a means of connecting the antennae 1 and 2 to the circuits 3 and 4. Such electric compensators (see Pierce, Electric Oscillations and "Electric Waves, Chapter XVL) produce a change in phase between the input current and the output current which, throughout the working range of the compensator, is proportional to the number of sections used. By providing suitable switches for introducing a larger or smaller number of sections in one or both of the compensators the difference in phase of the currents in circuits 3 and 4 may therefore be-adjusted to any desired value.

Instead of using an electric compensator between 1 and 3 or 2 and 4.1 may directly couple the circuits in each case and produce the desired phase changes by introducing suitable changes in the inductance, capacity and resistance of the circuits 3 and 4.

The circuit arrangements above described have been made cxtrcmcly simplc in order that the essential principle involved may not be obscured. It is obvious that the circuit arrangements might be modified in many ways without altering the method.

It will also be obvious that instead of heterodyning the two receiver circuils by a common I). M. F. and subsequently employing a compensator for bina'urally centering the beat tones, the same result may be accomplishcd by hetcrmlyning the two receiver circuits separately with individuals E. M. F.s 0f the same frequency but of adjustable phasc dili'crencc, .and effecting a binaural ccnteringot' (he beat tones in this manner by compensating for uhatevcr phase difference may exist between the antenna currents.

it will also be understood that my method 1. The method of determining phase difference between two alternating currents of the same frequency which consists of heterodyning each current with a third current. of different frequency and adjusting the phase of one or both of the first two currents until the two trains of beats are in phase.

2. The method of determining phase difference between two vibrations of the same frequency which consist of producing beats between each of these vibrations and a third vibration of different frequency, and adjusting the phase of one or both of the first two vibrations until the two trains of beats are in phase.

The method of determining phase'difference between two alternating currents which consists of heterodyning each current with a third current of different frequency and efiecting binaural centering of the two beat trains to determine the phase difference.

4. The methodof determining phase difference between two vibrations which con-- sists of producing beats between each of these vibrations and a third vibration of different frequency and determining the phase difi'erence between the two trains of beats by balancing.

5. The method of determining the direc-' tion of trains of waves which consists of receiving the waves on two spaced collectois, heterodyning each of the two currents produced with a third current and adjusting the phase of one or both of these received currents until the two trains of beats are in phase.

i 6. The method of determining phase difference which includes receiving wave trains on spaced collectors, heterodyning independently the wave trains received, and balancing to bring the resulting beat currents into phase.

7. The method of determining phase difference which includes receiving wave trains on two spaced collectors, heterodyning independently the received wave trains to produce beat tones, and binaurally centering the beat tones by balancing for the phase difference.

8. The method of determining phase dif ference which consists of receiving wave trains on two spaced collectors, heterodyning independently the two received wave trains with a single common source of oscillations and balancing to bring the currents into phase.

9. The method of determining phase difference which consists of receiving wave trains on two spaced collectors, heterodyning each received wave train with a local source of oscillations, rectifying the produced beat tones, and binaurally centering the beat tones by balancing for the phase difference.

10. The method of determining phase difference between radio frequency currents,

which consists-of receiving wave trains on two spaced antenna, rectifying the wave trains, heterodyningzthewave trains to produce beat tones, and binaurally centering the beat tones by balancing for the phase difference.

11. A system ference which includes a plurality of spaiced collectors, receiving circuits assoclated therewith, means for heterodyning the received currents, and balancing means for bringing the beat currents into phase.

12. A system of determining phase dii' ference which includes two spaced collectors, receiving circuits associated therewith, heterodyning means common to the two circuits, and balancing means for bringing the currents into phase:

13. A' system for determining phase difference which" includes two spaced collectors, receiving circuits associated therewith, means for heterodyning the received currents, balancing means for bringing the currents into phase, and a telephone receiver connected with each of the receiving circuits,

whereby the binaural sense may be employed for detecting a phase difference.

1d. Asystem for determining phase difofv determining phase dint- V rents, balancing means for bringing the cur- ERNEST MERRITT. 

